I thought about this while doing a mishmash of my two favorite Star Wars conversations right now: decrying Kylo Ren as a wasted talent badguy and character, and enjoying the crud out of Maul in animation.
So... I thought it might be fun to gather all the on-film students of Sidious and see how we’d rank them, both in terms of threat level, and in terms of coolness/iconic nature/just plain impressiveness as villains.
In the films, the guys who we see and know specifically as Sidious’s students/apprentices are these, in chronological order:
Maul
Dooku/Tyraanus
Anakin/Vader
Ben/Kylo (through Snoke his meat puppet)
So... if I had to give them a rank for threat level, I think I’d go with this:
1. Vader - He’s the man who carried out the Great Jedi Purge, was a relentless and ruthless military commander, was the most powerful of Sidious’s students when he turned, and even after being put in the suit, remained second only to the Emperor in terms of full dark side power. He also won his final duel with Dooku pretty handily, and was already able to tangle with him even when a hot headed a Jedi Apprentice. His one serious loss before Luke reached his peak training was to Obi-Wan, and that was due to a mistake on his part, one he specifically made sure to never repeat again, and Obi-Wan having the best style and knowledge a Jedi could hope for when facing young Vader.
2. Dooku - Dooku’s only serious loss ever was to Anakin at the height of his powers, and his prowess with the saber is canonically among the greatest on film (Sir Christopher’s age not withstanding). He also managed to be an effective lieutenant and partner to Sidious during their conspiracy during the Clone Wars, effectively acting as a political and military leader of the Separatists while managing it as a massive false flag operation. Where Vader is power and relentlessness, Dooku is finesse and deception.
3. Kylo - This one I’m not really enthusiastic about, as I think he’s easily the most unstable and foolish of the students, coasting far more on brute force and raw power than the others. Still, he has Skywalker-level strength, and was the First Order’s leader for a time. Having said that, I don’t know how he’d fair if he and the last contestant had equal resources...
4. Maul - ...Because Maul’s biggest drawback is that he was the subtle assassin and secret agent of Sidious when he was the apprentice, and thus never got to bask in the power of being charged with one of Sidious’s armies. Skill wise, he’s probably comparable to Dooku, since he managed to engage both Qui-Gon and Obi-Wan at the same time, though more susceptible to emotional instability when separated from his master, and has an Anakin style arrogance and mistake lead to him being almost a proto-Vader in defeat and suffering. Still, he’s eloquent, cunning, and scrappy as hell; he’s the only one of Sidious’s students to be cast aside and actually keep chugging along, and rather impressively manages to claw his way back to power, and actually survive being one of Sidious’s last real threats.
And in terms of coolness:
4. Kylo. He’s a bad copy of Anakin/Vader, and nothing more. He’s less sympathetic, less pitiable, less intimidating, less stable, and ultimately shoved into a role he’s ill suited for (male lead and protagonist, instead of villain).
3. Dooku. As awesome as Christopher Lee is, and as cool as his role in the Clone Wars is, he’s a placeholder Sith Lord.
2. Maul. Honestly, this guy was almost all style and looks at first. He wouldn’t really be closer to the top of this list if he weren’t resurrected for the cartoons... and then actually expanded on and fleshed out with skill. He’s basically Khan Noonien Singh as a Soth Lord, and with a somehow more traumatizing exile, and with a far more pitiable backstory. Seriously, he’s maybe the most pitiable character on this list - one gets the feeling that the biggest obstacle to him ever being redeemed is that he simply can’t conceive of the world in such terms, since he was raised from birth as Palpatine’s assassin and tool. And honestly, I’d kill to see them actually manage a live action blend of Ray Park and Sam Witwer’s performance.
1. Vader. Not a whole lot to get into specifically here. This character manages to be one of the most iconic in film history, and pulls double duty as a hero once and a villain later.